Brazed Hybrid Aluminum/Copper Heat Exchangers

The present description relates generally to methods and systems for hybrid aluminum/copper heat exchangers.

Heat exchangers may be formed of either aluminum (Al)/alloys of aluminum or copper (Cu)/alloys of copper. For some applications, Cu and/or alloys of copper may be preferred for higher thermal conductivity when compared to the thermal conductivity of Al and/or alloys of aluminum. However, Cu is heavier and more expensive than Al. For applications where cost and/or weight reductions are demanded, such as heat exchangers in vehicles, heat exchangers may include Al and/or alloys thereof to decrease cost and weight despite having a lower thermal conductivity.

Inventors have herein devised a solution to at least partially address the above problem. In one example, a system for a processed braze sheet (PBS) includes a processed braze sheet (PBS) including at least a layer of aluminum (Al) or aluminum alloy with at least one side comprising a melting point depressant (MPD) layer comprising copper (Cu). In this way, the low costs of Al may be utilized while the benefits of Cu are realized.

In one example, the MPD layer may be coated with a braze promoting (BP) layer. The BP layer may include one or more of nickel (Ni), cobalt (Co), and iron (Fe). The BP layer may be coated with a viscosity and/or a surface tension modifying (VM) layer comprising one or more of bismuth (Bi), lead (Pb), tin (Sn), antimony (Sb), and thallium (Tl). A location of the VM layer relative to the MPD layer and the BP layer may be altered to meet demands for different heat exchanger applications. By doing this, a cost of manufacturing a heat exchanger with properties of Cu may be decreased.

It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.

The following disclosure relates to a braze sheet. The disclosure provides support for different patterns of layers included in the processed braze sheet. Different processed braze sheet embodiments are shown in. A manufacturing process of a processed braze sheet is shown in.

illustrate different examples of braze sheets including different numbers of layers and materials within each layer. The braze sheet may include a core Al sheet material that is laminated or “cladded” on one or both sides by filler metal in one sheet. The laminated or cladded filler metal may be interchangeably referred to as “clad”. Components may be cut and formed out of the braze sheet and assembled for brazing in a furnace, during which only the clad melts and forms the braze joints of the heat exchanger. Additionally or alternatively, heat exchanger components may also be formed out of “core” or “clad” material in separate sheets. Additional steps or precautions are also taken to deal with the tenacious aluminum oxide that otherwise would hinder the clad from flowing to form braze joints, e.g. Nocolok flux brazing, vacuum brazing, and Ni—Al brazing.

Nocolok flux brazing may include a non-hygroscopic and a non-corrosive potassium fluoroaluminate flux which removes an oxide film on aluminum, and does not react with aluminum in the molten or solid state and whose residue is only slightly soluble in water. Vacuum brazing may be similar to fluxless brazing, which may eliminate a demand for post-braze treatments. During fluxless and/or vacuum brazing, furnace temperatures, surface cleanliness, and atmospheric purity may be maintained within tight tolerances.

The disclosure provides support for a method of manufacture to produce an aluminum, optionally including an aluminum alloy, braze sheet for use in mixed metal brazing in a furnace brazing environment such as controlled atmosphere brazing or vacuum brazing. The processed braze sheet (PBS) may be used without additional treatment or protocols in standard controlled atmosphere brazing furnaces, such as belt furnaces with an inert nitrogen atmosphere, or vacuum furnaces. The PBS may be used to braze Al to Al, Cu to Al and/or Ni to Al, in combination and all at once in the furnace to produce mixed metal heat exchangers for a vehicle. Some embodiments of the processed braze sheet also allow fluxless brazing of mixed metal heat exchangers. Herein, the braze sheet may include an alloy of aluminum that may be cladded on one or both sides. The PBS may define a material that includes the braze sheet undergoing a plating operation, as will be described herein.

The PBS may include a plurality of layers overtop of an aluminum braze sheet, which includes at least one Al4000-series layer. During processing of the aluminum braze sheet, up to three layers are added to at least one side of the Al4000-series layer. The three layers may include a melting point depressant (MPD) layer including Cu, a braze promoting (BP) layer including Ni, Fe, or Co, and a viscosity and/or surface tension modifier (VM) layer including bismuth (Bi) and/or lead (Pb) and/or other low melting elements as known in the art such as tin (Sn), antimony (Sb), and thallium (Tl). The MPD layer is situated underneath the BP layer, while the VM layer may be closer to the aluminum layer than the MPD layer, between the MPD and BP layers, or farther from the aluminum layer than the BP layer.

The MPD layer may depress the solidus of the clad from 577° C. to approximately 525° C. due to the formation of ternary Al—Cu—Si eutectic. This layer permits the brazing of Al to Al, Cu to Al and/or Ni to Al at temperatures below the clad melting point of 577° C. and, notably in the case of Cu to Al, below the temperature of the binary Al—Cu eutectic temperature of 548° C. Therefore, at brazing temperatures above approximately 525° C., the MPD layer may diffuse into the clad layer between the MPD layer and the Al layer and form liquid metal Al—Cu—Si ternary eutectic in-situ, which acts as the brazing filler metal during brazing. It is possible to braze functional heat exchangers with only the MPD layer, however, including the VM layer and, in the case of fluxless brazing, also the BP layer may enhance the heat exchanger. Face-to-face contact between the MPD layer and the clad may promote a more stable formation of Al—Cu—Si ternary eutectic. Therefore, the layer deposition method may not involve intermediate steps that deposit coatings between the clad and MPD layer, e.g. zinc coating before copper plating in the case of a plating deposition process. The benefit of this PBS is that such intermediate layers or steps are not demanded for good brazing, thus reducing manufacturing costs.

The BP layer may tolerate oxides during brazing via the exothermic reaction between Ni and liquid Al at braze temperatures. In this way, the BP layer may promote fluxless brazing. While the ternary Al—Cu—Si eutectic liquid produced with the MPD layer alone may percolate through oxides during brazing (and form braze joints), the oxides may form continuous sheets (as opposed to being broken or digested into the clad) which may pose as nucleation sites for crack formation and subsequent propagation. The BP layer may eliminate this phenomenon and promote formation of strong braze joints. A secondary benefit of the BP layer may be to protect the MPD layer underneath from partially oxidizing either during the processing of the PBS, or oxidizing in the furnace atmosphere due to trace amount of oxygen. In addition, it is noted that the BP layer may further depress the solidus of the clad to approximately 520° C. due to the formation of quaternary Al—Cu—Si—Ni eutectic liquid.

One or more VM layers may be included to modify the viscosity and/or surface tension of the liquid metal once formed, which aids in the capillary action of the molten clad, and thus promotes its flow at brazing temperatures. The VM layer comprises one or more elements from the group bismuth (Bi), lead (Pb), tin, antimony, and thallium, but preferably Bi and/or Pb. It is noted that Bi and/or Pb may mitigate shrinkage porosity that would otherwise be observed, and thus promote the formation of continuous braze fillets, with benefits to joint life, strength, and corrosion resistance.

While an embodiment with the BP layer and the VM layer configured as separate layers is practical, flexible, and functional, it is found that it is economical to combine the BP and VM layers into a single layer overtop the MPD layer, which may be referred to herein as the BPVM layer. Thus, overtop the clad or Al4000-series layer may include two layers: the MPD in face-sharing contact with the clad or Al4000-series of the braze sheet, and the BPVM layer directly overtop the MPD layer. This embodiment provides all the aforementioned benefits with decreased manufacturing costs and complexity. A processed braze sheet with MPD, BP, VM, and/or BPVM layers may be used to braze heat exchangers in controlled atmosphere furnace brazing or vacuum brazing operations without further treatment.

Turning now to, it shows a first embodiment of a braze sheet. The braze sheetmay include a first layer, a second layer, and a third layer. The first layermay be different than the second layer. The second layermay be different than the third layer. The second layermay be sandwiched between the first layerand the third layer. In one example, a first face of the second layeris in face-sharing contact with the first layerand a second face of the second layer, opposite the first face, is in face-sharing contact with the third layer.

In one example, the first layeris a core layer. The first layermay include an aluminum sheet material that is laminated or “cladded” on at least a first surface with the second layer. The second layermay be an alloy, different than the first layer, that may include a lower melting point than the first layer. The second layermay include one or more alloys of Al, Cu, and silicon (Si).

In one example, the third layeris a MPD layer including one or more of Cu, Bi, Pb, Sn, Sb, and Tl. The third layermay be configured to decrease the melting point of the second layer.

In one example, the first layer is an alloy of aluminum sheet (e.g., Al3000 or Al6000 series layer), the second layer is a clad (e.g., Al4000 series layer), and the third layer is a sheet comprising Cu or another metal.

Turning now to, it shows a second embodiment of a second braze sheet. The second braze sheetmay include the first layer, the second layer, and the third layer. As such, components previously introduced may be similarly numbered in this and subsequent figures.

In one example, the second layeris a first second layer, wherein the second braze sheetfurther includes a second second layer, identical to the first second layer. The second second layeris in face-sharing contact with an opposite side of the first layerrelative to the first second layer. As such, the first layeris sandwiched between the first second layerand the second second layer. In this way, the first layermay be laminated on both of its long sides. In this way, both sides of the first layerare cladded.

In one example, additionally or alternatively, the third layeris a first third layer, wherein the second braze sheetfurther includes a second third layer. The second third layermay be identical to the first third layer. The second third layermay be in face-sharing contact with the second second layer. In this way, the second second layeris sandwiched between the first layerand the second third layer.

Turning now to, it shows a third embodiment of a third braze sheet. The third braze sheetmay include the first third layer, the second third layer, and a fourth layer. In one example, the fourth layeris an aluminum-4000 series alloy.

In one example, the aluminum-4000 series layer may be an alloy of Al and Si included in the aluminum-4000 series, such as AL4343, Al4045, Al4047, and/or Al4150. The Si may depress the melting point of Al. For example, the melting point of Al may decrease from 660° C. to about 577° C. for 12.5 wt. % Si. Core Al alloys, such as the first layershown in, may include Al3000 or Al6000 series alloys, such as Al3003 or Al6061. The core Al alloy may include less Si than the Al-4000 series layer or may be free of Si.

Turning now to, it shows a fourth embodiment of a fourth braze sheet. The fourth braze sheetmay be similar to the first braze sheetofin that the fourth braze sheetincludes the second layersandwiched between the first layerand the third layer. Additionally, the first layeris laminated on only one side via the second layer. The fourth braze sheetmay further include a fifth layerand a sixth layer.

In one example, the fifth layermay be a braze promoting (BP) layer. The sixth layermay be a viscosity and/or surface tension modifying (e.g., VM) layer. The fifth layermay include Ni and the sixth layermay include one of more of Cu, Bi, Pb, Sn, Sb, and Tl. Additionally or alternatively, the fifth layermay be a VM layer and the sixth layermay be a BP layer.

Turning now to, it shows a fifth embodiment of a fifth braze sheet. The fifth braze sheetmay be similar to the fourth braze sheetin that it includes the first layer, the second layer, the third layer, a BP layer, and a VM layer. The fifth braze sheetmay be differentiated from the fourth braze sheetin that a seventh layerof the fifth braze sheetincludes a combination of the BP layer and the VM layer. In one example, the seventh layeris a BPVM layer integrally including a mixture of the BP layer and the VM layer.

Turning now to, it shows a sixth embodiment of a sixth braze sheet. The sixth braze sheetmay be similar to the fourth braze sheet, except that the sixth braze sheetdoes not include the sixth layer. As such, the fifth layermay be in face-sharing contact with only the third layeralong a first face and exposed at a second face opposite the first face.

Turning now to, it shows a seventh embodiment of a seventh braze sheet. The seventh braze sheetmay be similar to the fifth braze sheetin that it includes the first layer, the second layer, the third layer, and the seventh layer. The seventh braze sheetmay be differentiated from the fifth braze sheetin that the first layeris laminated on each of its long sides such that the seventh braze sheetincludes the first second layerand the second second layer. The seventh braze sheetmay further include the first third layerand the second third layer. The first second layeris sandwiched between the first layerand the first third layer. The second second layeris sandwiched between the first layerand the second third layer.

In one example, the seventh layeris a first seventh layer, wherein the seventh braze sheetfurther includes a second seventh layer. The first third layeris sandwiched between the first second layerand the first seventh layer. The second third layeris sandwiched between the second second layerand the second seventh layer. The first seventh layerand the second seventh layerare identical.

Turning now to, it shows an eighth embodiment of an eighth braze sheet. The eighth braze sheetmay be similar to the third braze sheetin that it includes the fourth layersandwiched by the first third layerand the second third layer. The eighth braze sheetfurther includes the seventh layerin face sharing contact with the first third layer. In this way, the first third layeris in face-sharing contact with and sandwiched between the fourth layerand the seventh layer.

In one example, the seventh layeris a first seventh layer, wherein the eighth braze sheetfurther includes a second seventh layer. The second seventh layermay be in face-sharing contact with the second third layer. In this way, the second third layeris sandwiched between the fourth layerand the second seventh layer.

Starting with an aluminum brazing sheet, the MPD and BPVM layers are added to the clad or Al4000-series layer by plating, which schematically involves up to three steps. A first step may include a mechanical and/or chemical pre-treatment of the Al brazing sheet to remove any existing aluminum oxide. A second step may include direct plating of Cu to form the MPD layer. A third step may include subsequent plating of Ni with co-deposited Bi and/or Pb to form the BPVM layer. As alluded above, the Bi and/or Pb can be plated as one or more separate VM layers, but it may be more efficient to co-deposit Bi and/or Pb along with Ni to form the BPVM layer.

The thickness of the MPD layer may be at least 20 μ″ thick. The amount of liquid filler metal generated in-situ when brazing below 577° C. may be proportional to the thickness of the MPD layer, and greater thicknesses may be used for some liquid filler metals to form in-situ depending on the application.

A thickness of the BPVM layer may be at least 5 μ″. The Bi and/or Pb content in the BPVM layer may be up to 20 wt %. If Bi and/or Pb are in a separate VM layer, then a target thickness may be determined based on a thickness of the BP layer such that the Bi wt % or Pb wt % falls in the ranges indicated. If separate BP and VM layers are used, the Bi and/or Pb wt % of the combined BP and VM layers would also be up to 20%.

Post-braze wt % ranges for processed brazed sheet (PBS), based on amalgamated layers from the outside edge of the material to the core portion of the material for, and through the entire material formay include Cu: 0.4-37%, Ni (or Co or Fe): 0.08-16%, Pb or Bi (or Sn or Sb or Tl): 0.002-3.4%, Si: 3.5-13%, and a remainder including Al+impurities.

The processed braze sheet (PBS) can be used directly in controlled atmosphere furnace brazing or vacuum brazing processes.

When using the PBS for the brazing of Al to Al, the brazing may occur with a brazing temperature between approximately 530° C.-610° C. Therefore, the PBS of the present disclosure enables low temperature brazing of Al, below the melting point of other clad alloys such as Al4343, Al4045 and Al4047. The PBS may be used in products as a drop-in replacement for aluminum braze sheets used in automotive heat exchanger manufacturing.

The PBS also provides enhanced brazing of Cu directly to Al, optionally including alloys of Cu and/or Al, on a clad side or clad sides of the PBS, with a brazing temperature between 530° C.-560° C. As such, Cu components may be brazed with Al assemblies in one brazing operation using the PBS. For example, a Cu component such as a turbulizer or other extended heat transfer surface may be brazed with an Al heat exchanger assembly to benefit from the higher thermal conductivity of Cu without having to braze a heat exchanger including only Cu or Cu alloy components. The PBS therefore can provide significant cost and weight advantages in the manufacturing of automotive heat exchangers.

Additionally, Ni and/or its alloys may be brazed to the clad side(s) of the Al PBS where the brazing temperature may be between approximately 530° C.-610° C. This may be useful in applications in which components of the HX are Ni-coated prior to assembly and subsequent brazing, for example a Ni-coated Cu turbulizer.

Turning now to, it shows a processing routinefor manufacturing the processed braze sheet embodiments of. A core sheet, such as the first layer, the fourth layer, and/or a braze sheet, may be pre-treated atto clean oxides from the braze sheet. The braze sheet may be clad on a single side or on both sides and may be similar to only the fourth layer, a combination of the first layerand the second layer, or a combination of the first layer, the second layer, and the second second layer. An MPD layer, such as the first third layeror the second third layer, may be joined to the core sheetat. In one example, the pre-treating and the MPD are applied to the braze sheet in a single step.

At, the sheet with the MPD (e.g., the PBS) may be stamped to form one or more components.

At, the components may be assembled with the stamped PBS and furnace brazed.

Prior to, if the BP and VM layers are desired, then the PBS may first be layered with a BP layer and then layered with a VM layer at, or vice versa. Adding the BP layer may include plating the MPD layer(s) with Ni and adding the VM layer may include plating the Ni layer(s) with Bi and/or Pb. Additionally or alternatively, a single BPVM may be plated onto the MPD layer(s) at.

Followingand/or, the braze sheet may be stamped and the resulting components may be assembled and brazed.

It will be appreciated that in embodiments where layers may be built up on one side of a starting layer of an Al sheet, it may be further possible that the same or different layers may also be built up on another side of the Al sheet. Some, but not all, envisioned examples of this have been included in the figures. Also, it is possible that multi-layer braze sheet (e.g., a starting material such as 4045/3003/4045) will be plated on only one side. Further, other scenarios include the possibility of the VM layer being above or below the BP layer, or between the MPD layer and the clad layer, even if these various scenarios are not specifically described.

The disclosure provides support for a system including a processed braze sheet (PBS) comprising at least a layer of aluminum (Al) or aluminum alloy with at least one side comprising a melting point depressant (MPD) layer comprising copper (Cu). A first example of the system further includes where the layer of Al is clad on at least one side with a metal alloy comprising a melting point lower than Al. A second example of the system, optionally including the first example, further includes where the layer of Al is Al4000-series comprising an alloy of Al and silicon (Si). A third example of the system, optionally including one or more of the previous examples, further includes where the MPD layer is coated with a braze promoting (BP) layer comprising one or more of nickel (Ni), cobalt (Co), and iron (Fe). A fourth example of the system, optionally including one or more of the previous examples, further includes where the BP layer is coated with a viscosity modifying (VM) layer comprising one or more of bismuth (Bi), lead (Pb), tin (Sn), antimony (Sb), and thallium (Tl). A fifth example of the system, optionally including one or more of the previous examples, further includes where the VM layer is between the MPD layer and the layer of Al. A sixth example of the system, optionally including one or more of the previous examples, further includes where the BP layer further comprises a viscosity modifying (VM) layer integrally arranged therein. A seventh example of the system, optionally including one or more of the previous examples, further includes where the MPD layer is between a VM layer and the layer of Al, the VM layer comprising one or more of bismuth (Bi), lead (Pb), tin (Sn), antimony (Sb), and thallium (Tl).

The disclosure provides additional support for a processed braze sheet (PBS) including a first layer clad along at least a first surface with a second layer, the first layer comprising at least aluminum (Al) and the second layer comprising a metal alloy with a melting point lower than Al and a third layer in face-sharing contact with the second layer, the third layer comprising copper (Cu). A first example of the PBS further includes where the second layer is a first second layer, and wherein the first layer is clad along a second surface with a second second layer. A second example of the PBS, optionally including the first example, further includes where the third layer is a first third layer, and wherein the second second layer is in face-sharing contact with a second third layer. A third example of the PBS, optionally including one or more of the previous examples, further includes where a braze promoting (BP) layer is in face-sharing contact with the third layer, the BP layer comprising one or more of nickel (Ni), Cobalt (Co), and iron (Fe). A fourth example of the PBS, optionally including one or more of the previous examples, further includes where the BP layer is in face-sharing contact with a viscosity modifying (VM) layer, the VM layer comprising one or more of bismuth (Bi), lead (Pb), tin (Sn), antimony (Sb), and thallium (Tl). A fifth example of the PBS, optionally including one or more of the previous examples, further includes where a viscosity modifying (VM) layer is integrally arranged within the BP layer, the VM layer comprising one or more of bismuth (Bi), lead (Pb), tin (Sn), antimony (Sb), and thallium (Tl). A sixth example of the PBS, optionally including one or more of the previous examples, further includes where the second layer further comprises silicon (Si).

The disclosure provides further support for a system including a processed braze sheet (PBS) configured for use by a heat exchanger, the PBS comprising a core layer comprising aluminum (Al), a melting point depressant (MPD) layer comprising copper (Cu) in face-sharing contact with a cladded side of the core layer, and one or more of a braze promoting (BP) layer and a viscosity modifying (VM) layer in face-sharing contact with the MPD layer. A first example of the system further includes where the BP layer comprises one or more of nickel (Ni), Cobalt (Co), and iron (Fe). A second example of the system, optionally including the first example, further includes where the VM layer comprises one or more of bismuth (Bi), lead (Pb), tin (Sn), antimony (Sb), and thallium (Tl). A third example of the system, optionally including one or more of the previous examples, further includes where the BP layer and the VM layer are combined and integrally arranged in a single BPVM layer. A fourth example of the system, optionally including one or more of the previous examples, further includes where the core layer is cladded on both sides, wherein the MPD layer is in face-sharing contact with both cladded sides.

show example configurations with relative positioning of the various components. If shown directly contacting each other, or directly coupled, then such elements may be referred to as directly contacting or directly coupled, respectively, at least in one example. Similarly, elements shown contiguous or adjacent to one another may be contiguous or adjacent to each other, respectively, at least in one example. As an example, components laying in face-sharing contact with each other may be referred to as in face-sharing contact. As another example, elements positioned apart from each other with only a space there-between and no other components may be referred to as such, in at least one example. As yet another example, elements shown above/below one another, at opposite sides to one another, or to the left/right of one another may be referred to as such, relative to one another. Further, as shown in the figures, a topmost element or point of element may be referred to as a “top” of the component and a bottommost element or point of the element may be referred to as a “bottom” of the component, in at least one example. As used herein, top/bottom, upper/lower, above/below, may be relative to a vertical axis of the figures and used to describe positioning of elements of the figures relative to one another. As such, elements shown above other elements are positioned vertically above the other elements, in one example.

In the present disclosure, the layers described are mutually exclusive, non-overlapping layers. Materials of one layer may not be mixed or dispersed with materials of another layer, unless explicitly disclosed. Each layer may be defined by boundaries, wherein adjacent layers with boundaries contacting one another may be in face-sharing contact.